The present invention relates to solvent-based pen inks.
Solvent-based pen inks are widely used in writing instruments, particularly in ball point pens. These inks generally include a resin binder, a colorant, e.g., a dye, and a solvent for the colorant. Because colorants are relatively expensive, it is generally desired to include as little colorant as possible without undesirably compromising the color intensity of markings made with the ink.
Acid dyes are desirable for use as colorants in pen inks, due to their good color intensity. Some acid dyes are useful in eradicable inks, i.e., inks that form markings that can be eradicated by writing over the marking with an eradicator fluid that includes a substance that can cause the dye to convert to a colorless form. Acid dyes are generally used only in aqueous inks, however, because they are not significantly soluble in many of the non-volatile organic solvents commonly used in ball-point pen inks. Because most aqueous inks are not suitable for use in ball point pens, acid dye-containing eradicable inks are generally not used in ball point pens.